1. Field of the Invention
The present invention relates to a method and an apparatus for fabricating a plasma display device, and more particularly, to a method of evacuating a plasma display device and filling it with a discharge gas and an apparatus for evacuating a plasma display device and filling it with a discharge gas.
2. Description of the Related Art
A plasma display device is a device for displaying images using gas discharge, and is spot-lighted as a display device which can replace a cathode ray tube (CRT) because the former has various excellent display characteristics such as resolution, luminance, contrast, latent image, and a view angle. In such plasma display device, discharge occurs in a discharge gas between electrodes by a DC or AC voltage applied across the electrodes, and a phosphor layer is excited by ultraviolet emission accompanying with the discharge to emit light rays.
FIG. 1 is an exploded perspective view schematically illustrating the structure of a conventional AC type plasma display device.
Referring to FIG. 1, transparent first electrodes 13a of display electrodes and second electrodes 13b of address electrodes are located between a front glass substrate 11 and a rear glass substrate 12. The first and second electrodes 13a and 13b are respectively located on the inner surfaces of the front and rear glass substrates 11 and 12 in stripe shapes, and are orthogonal with respect to each other when the substrates 11 and 12 are assembled. An dielectric layer 14 and a protective layer 15 are laminated on the inner surfaces of the front glass substrate 11 in sequence. On the other hand, at the rear glass substrate 12, partition walls 17 are formed on the upper surface of a dielectric layer 14', and cells 19 are formed by the partition walls 17. In addition, a phosphor layer 18 coats predetermined inside portions of the partition walls 17 forming the respective cells 19. An inert gas such as argon fills the cells 19.
The operation of the plasma display device configured as above is described as follows. First, a high voltage a so called trigger voltage is applied across the electrodes 13a and 13b to cause a discharge. When ions are accumulated in the respective dielectric layers 14 and 14', the discharge occurs. When the trigger voltage exceeds a threshold voltage, the discharge gas, such as argon, in the cell 19 goes into a plasma state by the discharge, and a stable discharge can be maintained between the electrodes 13a and 13b. In the stable discharge state, the rays in the ultraviolet range among rays emitted by the discharge collide with the phosphor layer 18 to emit light rays, and accordingly all pixels formed by the respective cells 19 display an image.
In assembling the plasma display device as above, after the electrodes, dielectric layers, partition walls, etc., are formed and the phosphor layer is applied, the substrates are bonded to each other. Air filled in the cells 19 of the display device right after bonding, and an air exhausting step is performed to remove the air and to fill the cells 19 with a discharge gas of argon. A vent hole is sealed after air exhaustion and filling of discharge gas.
In the conventional art, the air exhausting step is performed by connecting an exhaust pipe to a vent hole formed at a side of the substrate 12, and the plasma display device is heated simultaneously. That is, the inside of the panel is evacuated by a conventional vacuum pump via the exhaust pipe while the display device is heated. However, since the region of each cell 19 is a micro space whose width and height are in the range from several tens to several hundred micrometers, removing almost all the air contained in the cells 19 only by the vacuum pump is very difficult. Further, since the phosphor layer 18, partition walls 17, the protective layer 15 with a magnesium oxide material, etc. which are exposed to the cells 19 have surfaces with very complicated structures, and in particular the protective layer 15 has a characteristic of absorbing moisture, it is not easy to remove all materials absorbed in or combined to such surfaces in the air exhausting step. If the inside of the plasma display device is not evacuated sufficiently, there remains moisture, air, etc., within the panel, and these remaining materials bring a side effect of raising the voltage required for discharge, even though discharge begins within cells subsequently filled with a discharge gas. In addition, discharge in itself is impeded, and even though discharge occurs, sufficient ultraviolet rays cannot be emitted. Accordingly, the number of ultraviolet rays colliding with the phosphor layer decreases to lower the luminance.